The problem, however, is that when I connect the electrodes to my skin, I get a mild shock. I am powering the Arduino using an USB cable. I connected the grounds in the image to the Arduino's ground. I am guessing that the USB power is causing problems. Any suggestions on how to properly ground the Arduino? Also, I am not using any batteries in this circuit. The only power source is the USB cable that I use to power the Arduino. The +5 volt go to the Arduino's 5V pin and the ground ones go to the ground pin on the Arduino.